Field of the Invention
This invention relates to an air pressure control device for use in a testing chamber in which to conduct low pressure environmental tests of a self-propelled vehicle, especially an automobile, under assumed running of the vehicle on the terrain of higher altitudes.
FIG. 2 shows a conventional air pressure controlling system for setting the desired lower air pressure in the testing chamber.
Referring to FIG. 2, an automobile 21 is arranged in the low pressure environmental testing chamber 22 into which the outside air supplied by an air-supplying blower 25 via an air intake port 24 at the foremost part of an air supply duct 23 is introduced by way of a flow adjustment valve 26 and a throttle 27. The adjustment valve 26 is controlled by the output of a flow meter 28 connected parallel to the throttle 27.
An air pipe 29 for air discharging has a foremost air intake 30 positioned in the vicinity of a discharge opening of a discharge duct 21a of the automobile 21. The engine emission gases of the automobile 21 and the air in the testing chamber 22 are drawn by the pressure reducing air blower 32 by way of a pressure regulating valve 31 so as to be discharged by way of a silencer 33. The pressure regulating valve 31 is adjusted by output signals of a pressure sensor 34 provided in the testing chamber 22. A vacuum breaker 35 is provided between the pressure regulating valve 31 and the pressure reducing blower 32 so as to be in operation when the air pressure in the testing chamber 22 falls to lower than a prescribed lower value.
In the above described conventional air pressure controlling system, the air inlet 30 is opened in the vicinity of the discharge opening of the discharge duct 21a because of the necessity of discharging the engine emission gases out of the testing chamber. The engine emission gases and the air in the testing chamber 22 are discharged only by way of the air inlet 30 for setting the prescribed low air pressure in the testing chamber.
Thus the conventional control device has an inconvenience that the discharge opening of the discharge duct 21a is affected by the back pressure of the pressure reducing air blower 32. When the emission gases are discharged by way of the discharge duct 21a, these gases are introduced into the inlet 30 so that the intake volume of the air in the testing chamber is correspondingly reduced. Above all, when the r.p.m. of the automobile engine is changed abruptly, the air pressure at the discharge opening of the discharge duct 21a is subject to disturbances such that the air pressure at the discharge opening is no longer coincident with that in the testing chamber.
As a result thereof, the engine emission gases are discharged by way of the discharge opening of the discharge duct 21a at an air pressure different from that in the testing chamber 22 so that the testing can no longer be conducted under simulated natural environmental conditions.
Moreover, it has been difficult with the conventional control device to control the air pressure with high accuracy since the totality of the air passing through the air discharge pipe 29 is conveyed through the pressure regulating valve 31 so that it becomes necessary to use the valve of a larger size as the valve 31.